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WHAT IS AN ELECTRIC CURRENT IN ENGLISH LANGUAGE?
question is often asked: "What is an electric current?" No one has
ever seen it. We only know of the existence of a current owing to its effects.
A current can heat a conductor, it can have a chemical action when passing
through a solution, or it can produce a magnetic effect. We can measure
currents by observing their heating, chemical or magnetic effects. The practical
unit of current is called the Ampere.
things are necessary to cause an electric current to flow: first -
a complete circuit, and second - a driving force called the electromotive
force (e. m. f.).
you put free electrons on an insulated copper ball, what would they do? In this
case they would try to repel each other. In case you connected this charged
ball to another ball of equal size by a copper wire, what would be the result?
The electrons would move along the copper wire until the numbers of electrons
on each ball were the same. This is an example of electromotive force causing
a current to flow.
battery has a surplus of electrons on one of its two plates; so you say that a
battery furnishes an e. m. f. If a copper wire is run from one plate to the other, а
current flows in the complete circuit thus made. If a small bulb is placed in
the circuit, it will light up, giving evidence to a current flow. If the
battery were disconnected and a generator substituted for it, we should have a
typical lighting system. Both batteries and generators are the most common
sources of electromotive force. The practical unit of e. m. f. is the Volt.
Currents will flow more readily in some substances than in others, that
is, various substances offer lesser or greater resistance to the flow of
current. Such substances as porcelain, ebonite, rubber, glass and the like
having extremely high resistance are known as insulators. The practical
unit of resistance is the Ohm.
Substances whose properties lie between
those of conductors and insulators are called semiconductors. Let us name but
a few most widely used at present, they are germanium, silicon, selenium and
copper oxide. The importance of semiconductors in our life cannot be
overestimated. But for these tiny "workhorses" electronic industry
would not have achieved such a great progress.
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